Tilapines are the second most important group of farmed fish worldwide, with production of 2.5 million tons annually (Food and Agriculture Organization 2010), and they serve as a primary protein source in the developing world. The Sea of Galilee (Kinneret Lake) in Israel is one major source of commercial fishing. In recent years, the catch fish quantities have been subjected to a persistent decline.
Although the lake hosts some 27 species of fish, encompassing members of the families Cichlidae, Cyprinidae, Mugillidae, and Claridae, only a decrease in the catch of tilapines (Cichlidae) was noticeable. The main edible fish of the lake, Sarotherodon (Tilapia) galilaeus (St. Peter's fish), saw annual yields decreased from 316 tons in 2005 to 51, 8, and 45 tons in 2007, 2009, and 2010, respectively.
S. galilaeus contributes to the maintenance of the ecological balance of this lake. Hence, beyond its economic impact, the significant decline of St. Peter's fish populations, as well as the other lake tilapines (such as Tilapia zilli [common tilapia], Oreochromis aureus [Jordan tilapia], and Tristamella simonis intermedia) represents a definite threat to the entire ecosystem.
This decrease in the lake tilapine in the Sea of Galilee was due to a serious emerging disease in wild populations of tilapine species, including S. galilaeus, T. zilli, O. aureus, and T. simonis intermedia, and as well as in the pond-raised hybrid tilapia O. niloticus x O. aureus in Israel. The association of disease outbreaks with seasonality (May to October, when the water has relatively high temperatures) further indicated the involvement of an infectious agent, since water temperature affects the emergence of a wide range of parasitic, bacterial, and viral diseases of fish. Routine monitoring of known parasites, bacterial, viral pathogens or toxins did not reveal any abnormalities, and no causal agent was identified.
A similar outbreak of disease in tilapia was also found in Ecuador.
Thus, there was a need to identify the causal agent of this decline in tilapia populations in the two different geographical locations, as well as a need for tools and methods for detecting the presence of the causal agent within fish populations and protecting fish populations from the causal agent of this decline. This invention addresses these needs.